• Intel ring bus vs mesh

    Intel ring bus vs mesh

    The Scalable Processor family features fundamental changes to the web of interconnects that facilitate intra-processor and inter-socket communication. We also followed up in our Core iX review with more details, adding fabric latency and bandwidth tests to our analysis. More recently, though, Intel gave us extra info to flavor our take on the mesh. Several techniques have been used over the years for intra-processor communication. Intel's ring bus served as a cornerstone of the company's designs since Nehalem in With the ring bus, data travels a circuitous route to reach its destination.

    As you might imagine, adding stops on the bus amplifies latency. At a certain point, Intel had to split its larger die into two ring buses to combat those penalties. That created its own scheduling complexities, though, as the buffered switches facilitating communication between the rings added a five-cycle penalty. In the second slide, you can see Intel's mesh topology compared side-by-side to Broadwell-EX's dual ring bus design.

    Those processors feature up to 72 cores, so we know from practice that the mesh is scalable. For Skylake-SP, a six-column arrangement of cores would have necessitated three separate ring buses, introducing more buffered switches into the design and making it untenable.

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    As you can see, the latency-killing buffered switches are absent. The ability to stair-step data through the cores allows for much more complex, and purportedly efficient, routing. Intel claims its 2D mesh features a lower voltage and frequency than the ring bus, yet still provides higher bandwidth and lower latency. Of course, this allows the company to dedicate more of its power budget to completing useful work without sacrificing intra-die throughput.

    After all, mesh bandwidth also affects memory and cache performance. Intel constructs its Xeon Scalable Processors from different dies made up of varying core configurations. Intel isn't sharing transistor counts or die sizes at this time. The columns of cores are mirror images of each other with mesh pathways running along the right and left sides of the mirrored cores.

    This influences the distance between every other column of cores, which translates to more cycles required for horizontal data traversal. SNC provides increased performance in some scenarios, but Intel says it isn't as pronounced with the mesh architecture. In the past, the caching and home agent CHA resided at the bottom of each ring. Intel changed the CHA to a distributed design to mirror the distributed L3 cache.

    This helps minimize communication traffic between the LLC and home agent, reducing latency. With the Broadwell design, all PCIe traffic flowed into the ring bus at a single point, creating a bottleneck.

    The modular design provides multiple points of entry, alleviating the prior choke point. Two UPI links also share a single entry point at the top of a column. Models with a third UPI link have an additional entry point.A Bus topology is a network topology in which all nodes connect to the network via a central cable,called the bus.

    The bus acts as the shared communication medium that the devices are attached to. Any device that wants to communicate with other device on the network will send its data over the bus which will be send to all attached devices but the intended recipient will only process that packet. Thus bus topology is good and easy to setup for only a small number of devices, as devices and network utilization increases the performance issues and problems arise.

    intel ring bus vs mesh

    If the bus is damaged then the whole network fails making bus topology a less preferred option. All messages travel though the ring either in a clockwise direction or anti-clockwise direction. Ring topology is very rarely used today because they are expensive, difficult to install and manage. A failure in any single connection disrupts the ring topology thus also making ring topology a rare choice for network topologies.

    Star topology is the most common topology and is the widely implemented. In a Star Topology every device is connected to a central device such as a switch. Star topology requires more cable as compared to other topologies but it mode robust as a failure in one cable will only disconnect the specific connected computer via that cable to the central device.

    The messages between systems will always flow via the central device and so if the central device fails the entire network will fail. Star topology is very easy install, manage and troubleshoot making it the most common topology in home and office networks. In a Mesh topology nodes are connected to each other in a redundant fashion with multiple connections.

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    There are two types of mesh topologies, Partial and Full. In a full mesh topology all devices are connected to each other which is very expensive but provides the best redundancy as a failure of a single does not affect the network connectivity.

    In partial mesh devices partially connect with each other some devices have connectivity with some devices while others have different peers. There are several different paths available in mesh topology and nodes are intelligent devices like routes which can route packets on different algorithms such as Shortest Path First algorithm.

    The Internet is an example of partial mesh architecture. Today we covered a basic yet important lesson on network topologies. As we move ahead in Cisco CCNA certification learning we will see more lessons and technologies that require a firm understanding of this lesson.

    The Internet is an example of partial mesh architecture Figure below shows the mesh Partial topology architecture.Username or Email Address. This 8-core at the time monster was deemed too complex to live with a direct interconnect, shared bus, or other similar method of tying everything together.

    Better yet the bulk of the area it took was in metal layers so that saved a lot of die space. It was a good solution. By the time we got to Broadwell-EP things were a tad more complex with two rings and numerous bridges between them. That brings us to Knights Landing. As you can see from the picture KNL has a bunch of rings that form a mesh. Instead of each ring stop having two directions to choose from, there are now four.

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    Up and down is now up, down, left, and right. So rings scale, and that brings us to Skylake-EP. As you can see above, Skylake-EP has a mesh bus or more appropriately a lot of interconnected rings laid out like a mesh. That said if the latencies remain the same for each hop, again a theoretical assumption at this point, a mesh like configuration would drop the average latencies between stops by quite a bit.

    At that point they will turn and move horizontally until they hit the correct column, a method which reduces computation at each stop upping potential clocks quite a bit. So that is the major change in architecture from Broadwell-EP to Skylake-EP, rings and bridges are replaced by meshes. Going from linear to two-dimensional travel drops the number of average hops between any two points dramatically which should show up in latencies. Given the modest increases in core counts between generations it is going to be seen as lower latencies but as KNL points out, it will allow future Xeons to scale to 3x the current core counts or more.

    Better yet it tremendously increases cross-sectional bandwidths on the chip. Time to dig. Howdy, Guest. Subscriber log in: Username or Email Address Password.

    Jun 15, by Charlie Demerjian. Broadwell-EP block diagram By the time we got to Broadwell-EP things were a tad more complex with two rings and numerous bridges between them. S A The following two tabs change content below.Network topologies describe the methods in which all the elements of a network are mapped. The topology term refers to both the physical and logical layout of a network. In this network topology tutorial, we will explain: What is Topology?

    Types of Networking Topologies Two main types of networking topologies are 1 Physical topology 2 Logical topology Physical topology: This type of network is an actual layout of the computer cables and other network devices Logical topology: Logical topology gives insight's about network's physical design.

    In this method, the network consists of a direct link between two computers.

    intel ring bus vs mesh

    P2P Topology Diagram Advantages: This is faster and highly reliable than other types of connections since there is a direct connection. No need for a network operating system Does not need an expensive server as individual workstations are used to access the files No need for any dedicated network technicians because each user sets their permissions Disadvantages: The biggest drawback is that it only be used for small areas where computers are in close proximity.

    You can't back up files and folders centrally There is no security besides the permissions. Users often do not require to log onto their workstations. Bus Topology Bus Topology Diagram Bus topology uses a single cable which connects all the included nodes.

    The main cable acts as a spine for the entire network. One of the computers in the network acts as the computer server. When it has two endpoints, it is known as a linear bus topology. Famous for LAN network because they are inexpensive and easy to install.

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    It is widely used when a network installation is small, simple, or temporary. It is one of the passive topologies. So computers on the bus only listen for data being sent, that are not responsible for moving the data from one computer to others.

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    When network traffic is heavy, it develops collisions in the network. Whenever network traffic is heavy, or nodes are too many, the performance time of the network significantly decreases. Cables are always of a limited length. Ring Topology Ring Topology Diagram In a ring network, every device has exactly two neighboring devices for communication purpose. It is called a ring topology as its formation is like a ring. In this topology, every computer is connected to another computer.

    Here, the last node is combined with a first one. This topology uses token to pass the information from one computer to another.

    In this topology, all the messages travel through a ring in the same direction. Adding or deleting a device in-ring topology needs you to move only two connections.When Intel makes a fundamental shift in architecture, it can have a major impact on an industry. While in the 4 core days of Nehalem this worked well, Intel finally hit its limits with the Intel Xeon E V4 generation.

    Today the company is announcing that its next-generation products will use a mesh architecture for on-die communication.

    The two rings allowed for information to transfer in either direction using the two bridges to transport between the two sets of cores. This structure is incredibly important. Every time data needed to traverse to different parts of the die, it would have to hop along these rings. Each hop adds latency and there was a natural wire limitation to bandwidth. What this meant is that communication between hops on the rings could vary significantly on higher core count parts.

    Hops not only coincide with cores, but there are also stops on the rings for PCIe and memory controllers. Here is an example from the Haswell generation E7 V3 where the rings had only 18 cores to deal with but you can see the additional QPI link added for 4 socket and above connectivity:.

    Intel® Xeon® Processor Scalable Family Technical Overview

    It is easy to see how this complexity with so many cores was becoming a constraint. Remember, this architecture debuted with a 4 core part and scaled to about 6x the complexity with some obvious modification.

    For the higher core count parts, Intel needed a change. That change is mesh. It turns out, there are only so many ways that these problems are solved. One of them could have been adding more bridges and more rings. We will have a more complete version that we can share during the launch coverage.

    intel ring bus vs mesh

    While this is vague in places it does not need to be, it does help present a simple diagram for Skylake-SP and presumably future Intel architectures such as Coffee Lake. The basic premise of the above is that there are vertical and horizontal connections. The key here is that instead of two sets of rings, the number of on-die communication channels Intel is opening up is exploding.

    This is done both to significantly increase on-die bandwidth but also to decrease latency between most points of the chip. Every time one needs to traverse to a new wire or hop, there is a clock cycle penalty.

    Although the Skylake diagram is conceptual, it does allow you to understand how it will work in practice. Implications of this new mesh architecture are severalfold. On the PCIe side, there is an important nuance depicted.

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    Contrast this with Broadwell where there was only one stop for PCIe on one of the ring sets. If you look at where the ring connects to the PCIe in Broadwell, you can see a potential bottleneck where there is one connection point to only one set of rings.

    With the new mesh architecture, there will be multiple PCIe termination points connected to the mesh.

    That means transfers over PCIe should be more efficient. At the end of the day, there were a number of architectural changes that needed to happen after Broadwell. Even in smaller CPUs, we saw similar behavior.

    Intel "mesh" vs intel "Ring"

    In the end, as chips become more complex, Intel needed a way to manage the complexity of having more resources connected at the heart of servers. The next generation of that management is through the new mesh architecture. DC — you are exactly right. KNL also used a mesh.A few weeks ago we were allowed to discuss the new Intel mesh interconnect architecture at a high-level.

    The mesh architecture is a cornerstone, so important that it can have dramatic impacts on performance. The first concept we wanted to cover is the Intel Mesh Interconnect Architecture and why it is moving away from rings.

    As we covered in our previous piece, the ring architecture was the product of a much smaller topology.

    intel ring bus vs mesh

    Moving to a mesh interconnect aligns resources in rows and columns yielding higher overall bandwidth and lower latencies than Intel could have achieved with its older rings scaled up yet again. That is important for our discussion of mesh as it is comparable to the third UPI link in the Xeon Platinum and the top end of the Gold range. Also, before we get too far ahead of ourselves, we will often use the 28 core die in our examples.

    These have less complex structures. Two items are missing from the smaller die mesh diagrams. Those Cables on the Skylake-F look innovative. Sign me up for the STH newsletter! Sunday, April 12, Server Server CPUs.

    Things are getting Meshy: Next-Generation Intel Skylake-SP CPUs Mesh Architecture

    Intel Mesh Architecutre V Ring. Thanks again Patrick, for all these Articles. Please enter your comment! Please enter your name here. You have entered an incorrect email address!Forums New posts Search forums. New posts New posts New profile posts Latest activity. Members Current visitors New profile posts Search profile posts. Log in Register. Search titles only. Search Advanced search…. New posts. Search forums. Log in. Contact us. Close Menu.

    JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding. Joined Feb 20, Messages Joined Sep 13, Messages 21, Are they basically different implementations of the same thing? Joined Apr 3, Messages 1, I don't know if it's ever been discussed together, but I wanted to link them. PCIe 4 is coming. Same number of lanes, just higher speed? AlexisRO Limp Gawd. Joined Feb 27, Messages Joined Feb 6, Messages 1, I was going to compare the two approaches and then it struck me I have no clue where Intel plumbed in the L3 on the new mesh interconnect.


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